LED high-voltage linear constant current technology is widely used for the advantages of simple schema, low cost, no high frequency transformer and no EMC problem etc. and is increasingly applied to LED controllable silicon dimming
LED linear constant current circuit currently existed in market is shown in FIG. 1, inputting alternating current voltage source is connected with the positive end of the LED light string 104 after rectification by the rectifier bridge 101, the negative end of the LED light string 104 is connected with the master chip 102, current flowing through the LED light string 104 is controlled by the master chip 102 and the current adjustment resistance 103, the output current is controlled by maintaining the current control chip and maintaining the current adjustment resistance. A problem for the existing circuit is inconstant output power that varies with the variation of busbar, when the voltage of the busbar is higher than the voltage drop of the LED light string and the initiation voltage of the chip, a constant current output can be achieved, however, when the voltage of the busbar is lower than the voltage drop of the LED light string and the initiation voltage of the chip, the light string cannot be turned on to light, by this operating way, actual average current value of the LED lamp is inconsistent so that a constant power output cannot be achieved under different output voltage and different groups of LED lamps.